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Centrifuge and Vacuum Drying Q&A

  •   What is the typical consistency of a product dried upon a centrifuge? Is it powdery and free flowing or is it clumpy and requires some type of deagglomeration?

    There is no one “typical consistency” but in general a filtering centrifuge will accept a slurry (i.e., a suspension of solid particles  in a liquid) that has anywhere from 5 % to 50 % +/- solids (but more commonly in the 15 % to 30 % range) and produce a wet cake that has LOD (loss on drying) 10 % to 40 % +/- moisture in the discharged “cake” (as the solids coming out of the filtering centrifuge are sometimes called). The solid particles, to be filterable, are usually in the “micron range”, i.e., anywhere from a few microns to few thousand microns, depending upon the application and the filtering centrifuge being used.

    Again, it could be powdery and free flowing in some applications, especially if the moisture level gets down dry enough and the particles do not clump together, or it may in some cases, not be as powdery and free flowing. There is a wide range of possible applications that can be processed through a filtering centrifuge. Get in contact with a reputable manufacturer with process know-how and a test center, where testing can be conducted and behavior of the solids in a controlled environment can be observed. The data collected from several test-runs can then be used for scale-up to a production size centrifuge.

  •   Please enlighten me on how to determine the end point of a drying powder. This relates to not getting the temperature too high for heat labial compounds.

    Assuming the question pertains to a vacuum dryer, as the powder being dried reaches the final drying stages, its temperature spikes up, indicating the end-point in its drying cycle. As such, constantly monitoring product temperature is critical to drying a heat-sensitive powder.

  •   What are some factors in deciding what centrifuge type to select?

    There are several, the most important among them are aspects of the slurry that will indicate how well it will either filter or sediment, such as the morphology of the solid particles, the particle size distribution, concentration in the feed stream, viscosity of the liquid, and about a dozen other factors. It is best to work with an expert and go over these major and minor aspects since a good understanding of the process, followed by lab testing and evaluation, is necessary for the right selection of the equipment, which can mean significant installation, operational and maintenance cost savings over the 30+ year life of the machine.